arXiv subjects

I. Millán-Irigoyen

Publications and source records attributed to I. Millán-Irigoyen.

6 recordsLinked to original sources

arXiv2026

MEGARA Stellar Spectral Library. Second Release

We present the second release of the MEGARA spectral library, MEGASTAR, which now includes all spectra collected during ten observing semesters at the Gran Telescopio CANARIAS. This new release supersedes our first release and incorporates a substantial number of additional observations (2000 new spectra), obtained at high spectral resolution, R(FWHM)$\sim$20000, in two wavelength ranges centred on H$α$ (6420 - 6790 A) and on the CaII triplet (8370 - 8885 A). The aim of this paper is to introduce MEGASTAR DR2 to the community as its high-resolution spectra can serve as a valuable resource for numerous types of research. In particular, we will use MEGASTAR spectra to construct SSP blocks within the HR-PyPopStar evolutionary synthesis models. The stars were observed using the integral field spectroscopy mode of the instrument. We process the data in a uniform way with the MEGARA data reduction pipeline. We estimate the stellar flux by adding the spectra from 37 spaxels, centred on the spaxel with the highest flux in the IFU reconstructed image. This approach guarantees that the effective slit width, and therefore the spectral resolution, are the same for all spectra. The second MEGASTAR release consists of 2838 spectra corresponding to 1408 stars, providing a better coverage of the stellar parameter space than the first release. The spectra were acquired with an average continuum S/N of about 215. This second release meets the standards of a modern empirical library: it offers reliable calibrations, data free from slit effects, observations of a large number of stars, and provides high spectral resolution to model both individual stellar clusters and entire galaxies observed with MEGARA.

astro-ph.SR↗

arXiv2025

HR-pyPopStar II: high spectral resolution evolutionary synthesis models low metallicity expansion and the properties of the stellar populations of dwarf galaxies

Low metallicity stellar populations are very abundant in the Universe, either as the remnants of the past history of the Milky Way or similar spiral galaxies, or the young low metallicity stellar populations that are being observed in the local dwarf galaxies or in the high-z objects with low metal content recently found with JWST. Our goal is to develop new high-spectral-resolution models tailored for low-metallicity environments and apply them to analyse stellar population data, particularly in cases where a significant portion of the stellar content exhibits low metallicity. Methods. We used the state-of-the-art stellar population synthesis code HR-pyPopStar with available stellar libraries to create a new set of models focused on low metallicity stellar populations. We have compared the new spectral energy distributions with the previous models of HR-pyPopStar for solar metallicity. Once we verified that the spectra, except for the oldest ages that show some differences in the molecular bands of the TiO and G band, are similar, we reanalysed the high resolution data from the globular cluster M 15 by finding a better estimate of its age and metallicity. Finally, we analysed a subsample of mostly star-forming dwarf galaxies from the MaNGA survey we found similar stellar mass-mean stellar metallicity weighted by light to other studies that studied star forming dwarf galaxies and slightly higher mean stellar metallicity than the other works that analysed all types of dwarf galaxies at the same time, but are within error bars.

astro-ph.GA↗

arXiv2024

Chemical evolution models: the role of type Ia supernovae in the $α$-elements over Iron relative abundances and their variations in time and space

The role of type Ia supernovae (SN Ia), mainly the Delay Time Distributions (DTDs) determined by the binary systems, and the yields of elements created by different explosion mechanisms, are studied by using the MulChem chemical evolution model applied to our Galaxy. We explored 15 DTDs and 12 tables of elemental yields produced by different SN Ia explosion mechanisms, doing a total of 180 models. Chemical abundances for $α$-elements (O, Mg, Si, Ca) and Fe derived from these models are compared with recent solar region observational data of $α$-elements over Fe relative abundances, [X/Fe], as a function of [Fe/H] and age. A multidimensional maximum likelihood analysis shows that 52 models are able to fit all these datasets simultaneously, considering the 1$σ$ confidence level. The combination of STROLG1 DTD and LN20181 SN Ia yields provides the best fit. The exponential model with very prompt events is a possible DTD, but a combination of several channels is more probable. The SN Ia yields that include MCh or Near MCh correspond to 39 (75%) of the 52 best models. Regarding the DTD, 31 (60%) of the 52 most probable models correspond to the SD scenario, while the remaining 21 (40%) are based on the DD scenario. Our results also show that the relatively large dispersion of the observational data may be explained by the stellar migration from other radial regions, and/or perhaps a combination of DTDs and explosion channels.

astro-ph.GA↗

arXiv2022

MEGASTAR (III). Stellar parameters and data products for DR1 late-type stars

MEGARA is the optical integral field and multi-object spectrograph at the Gran Telescopio Canarias. We have created MEGASTAR, an empirical library of stellar spectra obtained using MEGARA at high resolution $R=20\,000$ (FWHM), available in two wavelength ranges: one centered in H$α$, from 6420 to 6790\,Å and the other centered in the \ion{Ca}{ii} triplet, from 8370 to 8885\,Å (\mbox{HR-R} and \mbox{HR-I} VPH-grating configurations). In this work, we use MEGASTAR spectra, combination of these two short wavelength intervals, to estimate the stellar parameters namely effective temperature, surface gravity and metallicity (and their associated errors) for a sample of 351 MEGASTAR members with spectral types earlier than B2. We have applied a $χ^2$ technique by comparing MEGASTAR data to theoretical stellar models. For those stars with stellar parameters derived in the literature, we have obtained a good agreement between those published parameters and ours. Besides the stellar parameters, we also provide several products like the rectified spectra, radial velocities and stellar indices for this sample of stars. In a near future, we will use MEGASTAR spectra and their derived stellar parameters to compute stellar population evolutionary synthesis models, which will contribute to a better interpretation of star clusters and galaxies spectra obtained with MEGARA.

astro-ph.SR↗

arXiv2021

HR-pyPopStar: high wavelength-resolution stellar populations evolutionary synthesis model

We present the HR-pyPopStar model, which provides a complete set (in ages) of high resolution (HR) Spectral Energy Distributions of Single Stellar Populations. The model uses the most recent high wavelength-resolution theoretical atmosphere libraries for main sequence, post-AGB/planetary nebulae and Wolf-Rayet stars. The Spectral Energy Distributions are given for more than a hundred ages ranging from 0.1 Myr to 13.8 Gyr, at four different values of the metallicity (Z = 0.004, 0.008, 0.019 and 0.05), considering four different IMFs. The wavelength range goes from 91 to 24 000 Å in linear steps δλ = 0.1 Å, giving a theoretical resolving power R_{th,5000} ~ 50 000 at 5000 Å. This is the main novelty of these spectra, unique for their age and wavelength ranges. The models include the ionising stellar populations that are relevant both at young (massive hot stars) as well as old (planetary nebulae) ages. We have tested the results with some examples of HR spectra recently observed with MEGARA at GTC. We highlight the importance of wavelength-resolution in reproducing and interpreting the observational data from the last and forthcoming generations of astronomical instruments operating at 8-10m class telescopes, with higher spectral resolution than their predecessors.

astro-ph.GA↗

arXiv2020

Chemical evolution of galaxies: emerging dust and the different gas phases in a new multiphase code

Dust plays an important role in the evolution of a galaxy, since it is one of the main ingredients for efficient star formation. Dust grains are also a sink/source of metals when they are created/destroyed, and, therefore, a self-consistent treatment is key in order to correctly model chemical evolution. In this work, we discuss the implementation of dust physics into our current multiphase model, which also follows the evolution of atomic, ionised and molecular gas. Our goal is to model the conversion rates among the different phases of the interstellar medium, including the creation, growth and destruction of dust, based on physical principles rather than phenomenological recipes inasmuch as possible. We first present the updated set of differential equations and then discuss the results. We calibrate our model against observations of the Milky Way Galaxy and compare its predictions with extant data. Our results are broadly consistent with the observed data for intermediate and high metallicities, but the models tend to produce more dust than observed in the low metallicity regime.

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